Dock levelers are utilized to compensate for height differences between the dock platform and the bed of a parked vehicle to permit forklift trucks and personnel to readily move on and off the vehicle during loading and unloading operations. A typical dock leveler has a dockboard or deck pivotally hinged at its back edge for varying the height of the dock leveler in order to compensate for the height differences. An extension plate or lip is typically hinged to the front edge of the deck for spanning the distance between the rear end of the vehicle bed and the outer front edge of the deck. The lip is adapted to move relative to the deck front edge between a pendant stored position, an extended preparatory position, and a lowered operative position. In its operative position, the lip extends from the deck front edge and may be substantially coplanar with the upper surface of the deck. The lip rests upon and is supported by the upper surface of the bed of the parked vehicle. Thus the extended lip spans the gap which is formed between the rear edge of the vehicle bed and the front edge of the deck.
To move the lip from the pendant stored position to an extended operative position, the deck is normally pivoted upwardly a sufficient amount whereby the lip can swing outwardly to the extended preparatory position without obstruction from the parked vehicle. Once the lip has cleared the parked vehicle, the deck and extended lip are pivoted downwardly as a unit until the extended lip rests upon the vehicle bed in the operative position. After loading or unloading of the parked vehicle has been completed, the vehicle is moved away from the dock permitting the lip to be cycled to assume its pendant stored position.
In some conventional dock leveler assemblies, heretofore, a safety hazard may be created when the dock leveler was activated without a vehicle in position or when the vehicle moved away from the dock after completion of the loading or unloading operation because the lip of the assembly remained in an extended outwardly projecting position with respect to the dock platform. In such a situation, if the operator failed to take the necessary steps to return the dock leveler and lip to their stored position, the extended outwardly projecting lip was very susceptible to being struck or damaged by the next vehicle backing towards the dock for loading or unloading. Thus, to avoid such a situation, it required a conscious action on the part of the dock personnel as well as alertness on the part of the vehicle driver.
Attempts to provide a lip which would automatically assume the pendant stored position without conscious action by the dock personnel have not been fully satisfactory. Many conventional dock levelers have required a relatively large deck lift spring biasing force to extend the lip thus requiring a large force to walk down the ramp to the truck bed. Some of the typical dock leveler assemblies which have utilized gravity to move the lip from the extended position to the fully pendant position have been unable to move the lip the necessary amount after the lip has pivoted through the first portion of its downward travel due to insufficient gravitational force. Other difficulties have resulted from the premature pivotal movement of the lip from its extended position before it is brought into supporting engagement with the bed of the parked vehicle. Other devices have been highly susceptible to malfunction or are difficult and awkward to install and maintain in proper working order.